A microkeratome is a surgical implement for performing lamellar refractive surgery, and in particular lamellar keratectomy. This procedure involves the resection of an outer layer of the patient's cornea. As can be appreciated, the depth of the resection must be carefully controlled to ensure a successful operation.
A microkeratome 200 as disclosed, for example, in U.S. Pat. No. 5,133,726 to Ruiz et al. includes a blade 202 to remove an outer layer c' of the cornea C (FIG. 27). Blade 202 is held by a skate 207 which is slidably attached to the top 209 of a ring 210 by a pair of dovetail runners 212. The ring 210 is set over the cornea such that an outer portion of the cornea extends upward above the ring. A shim member 215 is releasably received in a slot 217 along a bottom portion of the skate to engage the cornea. The thickness t of shim 215 sets the vertical distance d between the cutting edge 220 of blade 202 and the bottom surface 222 of shim 215, which in turn, sets the depth of the resection. Shims having different thicknesses can alternatively be received in slot 217 to vary the depth of the cut.
While the components of the microkeratome are fabricated according to precise manufacturing techniques, a surgeon needs to ascertain with certainty the actual depth of the cut which will be effected with a particular shim. Surgeons have not, heretofore, been able to consistently and accurately measure the blade extension; and therefore have been forced to rely solely upon the manufacturer's calibration of the shims.
Further, the use of replaceable shims enables only a finite adjustment of the blade extension. As a result, the options available to the surgeon for a prospective operation are limited. Also, the need for multiple alternative shims requires the manufacture of a number of additional parts--many of which are unused in any one operation. As can be appreciated, this manufacture of alternatively used parts increases the costs of making the microkeratome.